The present invention relates to a digital frequency synthesizer which is immune to small variations of an analog program control signal to maintain the frequency division ratio constant when the variations lie within a predetermined range.
Conventional frequency synthesizers of the type which employs a programmable frequency divider make use of an analog-to-digital converter for converting an analog program control signal into a digital signal for controlling the frequency division ratio of the programmable frequency divider. However, the inherent small variation of the analog control signal tends to adversely affect the frequency division ratio.